The field of the invention deals with the attachment of components to a substrate by deformation of a lead protruding through a hole and from the side of the substrate opposite from the side on which the component is located. More particularly, the invention is directed to mounting of electrical components on circuit boards by deforming a lead portion of the component which protrudes from an underside of the circuit board.
Generally, electrical components are attached to a circuit board by inserting at least one lead thereof through a hole of the circuit board until the body of the component engages a top surface of the circuit board and trimming the lead tip to a preferred length and clinching or bending the lead away from the longitudinal axis thereof. Upon populating a circuit board with a particular number of electrical components in this manner, a more permanent attachment is provided by applying solder to the leads, as by a wave soldering process or the like.
As the density with which components are mounted upon a circuit board increases, the space available for inward or outward clinching of the leads decreases, especially when one considers the sizes and configurations of the tooling used to accomplish this clinching, as exemplified in the U.S. Patents cross-referenced above.
The above cross-referenced Japanese Application is exemplary of a prior art attempt at attaching a component to a circuit board by swaging the lead and providing burrs or portions extending beyond the diameter of the hole in order to retain the component on the board. The Applicant of the instant invention made several attempts at similar approaches and noted deficiencies therein. For instance, the standard paractice is for the diamter of the circuit board hole to be at least 0.015 inches greater than that of the corrsponding lead in order to provide for proper and reliable automated insertion of the lead into the hole. A 0.020 inch lead was inserted in a 0.035 inch hole, and the protruding tip of the lead was totally mashed or coined down to 0.005 inches thickness and there was still not enough lateral spreading of the material of the lead to provide for an attachment similar to that of the Japanese application. In other words, the diameters of the leads and holes would have to be much closer in size than those generally used in the industry at this time, resulting in much closer tolerances for insertion of the leads into the holes.
Still further, swage tooling changes would have to be made more frequently according to changes in the lead and hole diameters, or accomodation would have to be made in the swage tooling to provide a lead-in surface at the top thereof to be able to accomodate the leads of different diameters. However, by providing such a lead-in, the component is movable parallel to the longitudinal axis of the lead, according to the depth of the lead-in surface, after swaging and prior to soldering.
Accordingly, it is an object of the invention to provide a reliable means for attaching a component to a circuit board by deforming at least one lead thereof and wherein the spacing between hole centers on the board may be as close as 0.100 inches. Still further, it is an object of the invention to provide such a device wherein the trimmed and deformed lead generally does not extend out of the area of plating of the hole, in order that less solder may be used in attaching the component more permanently to the circuit board and in order that the components may be mounted on the circuit board with a higher density and less chance of bridging between solder points.
Still further, it is an object of the instant invention to reduce the solder point protruding from the circuit boards such that closer back-to-back spacing of circuit boards may be accomodated.
It is another object of the instant invention to provide a tooling for trimming and deforming a lead tip in order to attach a component to a circuit board whereby the footprint presented by the tooling is such as to eliminate interference with an already-mounted lead in an adjacent hole.
Accordingly, the instant invention comprises an arrangement, for each lead to be trimmed and deformed, of a fixed tool and a cooperating pivotal tool whereby the lead tip protruding from the underside of the circuit board is trimmed to a preferred length and split generally longitudinally thereof into at least two furcations which are displaced laterally of a longitudinal axis of the lead in order to hold the component on a circuit board. Preferably, the lead has been inserted sufficiently into the circuit board for the component to abut against an upper surface of the circuit board so that the lead deformation on the underside of the circuit board will hold the component body against the upper surface of the circuit board while stabilizing the component thereon. When used on a radial lead or axial lead component having two leads, the method and apparatus of the instant invention may be utilized to provide that such a component will be stabilized and not rock about as may occur in some instances with the standard inward or outward clinch.